This invention relates to textile pigment printing, and in particular to the production of a printed textile fabric wherein the printed areas are opaque and are thus substantially unaffected by the color of the underlying yarns.
Textile pigment printing, by definition, involves the printing of an insoluble coloring material (pigment) on selected areas of a textile fabric. The pigment, which has no affinity for the fibers of the fabric, is adhered to the fabric by a resin binder. The term "resin-bonded pigment" is often applied to this type of textile printing process and product.
In conventional textile pigment printing operations, the pigment colorants and resin binder are in an aqueous emulsion in the form of a thick printing paste, and this printing paste is applied to the fabric by patterned rollers or by screens. After the paste is printed onto the fabric, the fabric is subjected to heat to dry and cure the resin binder.
In conventional resin-bonded pigment prints of this type, the printed areas are relatively transparent. While the pigments serve to color the yarns, the underlying color of the yarn shows through. For this reason, conventional pigment printing is usually done on an uncolored or white fabric, or on pastel shades. When conventional pigment printing is done on predyed fabrics, it is generally restricted to the printing of darker colors over a lighter background color. Conventional pigment print pastes, when applied to deep shades, do not produce an acceptable appearance. Due to the highly transparent nature of the conventional pastes and incomplete encapsulation of the surface fibers of the yarns, the color of the fabric ground shade is apparent through the pigment paste, which results in a severe change in shade of the desired printing color. For example, on a white or pastel colored fabric, the printing of a bright red print paste will remain bright red on the fabric; however, when printed on a black fabric, it will not produce the desired bright red shade. Instead, the printed area will be almost indistinguishable from the black ground shade.
Prior attempts have been made to overcome the effect of darker ground shades and to produce an opaque print by applying the printing paste to the fabric in a layer sufficiently thick or dense to completely cover and hide the underlying yarns. However, the resulting product exhibits poor appearance and poor washfastness properties. French Pat. No. 2,402,733, published Apr. 6, 1979, for example, mentions the possibility of adding titanium dioxide pigments to conventional print pastes to achieve the necessary opacity to print light shades on darker ground shades. The patent goes on to teach, however, that this approach is not satisfactory in that the paste was not sufficiently bonded to the support and simply made a crust on its surface. Further, the printed fabric had an unpleasant hand and exhibited poor washfastness and poor fastness to dry cleaning. To overcome these problems, the patent describes the use of a butadine based copolymer in combination with titanium dioxide pigments for opacity, applied to superficial areas in the immediate vicinity of the face of the fabric. However, fabrics produced in accordance with the teachings of the French patent have been shown to exhibit poor washfastness and durability. The patent does not teach the importance of encapsulation and coating of the exposed surface portion of the yarns and the individual fibers present at the surface of the yarns.
Furthermore, a further and very significant limitation of this formulation is its inability to produce shades with high color saturation (chroma). Although titanium dioxide serves as an effective opacifying pigment for printing a white or pastel area, its usefulness as an opacifying agent is severely limited when deep shades with high chroma are desired for the printed area. When mixed with colored pigments of the desired hue, the bright white titanium dioxide pigment will lower the apparent chroma of the paste, resulting instead in a subdued pastel coloration rather than the desired bright color of the added pigment.
It is an object of the present invention to provide an improved opaque printing formulation which provides opaque printed areas with significantly increased chroma (color saturation).
A further object of this invention is to achieve this high degree of opacity and chroma while maintaining the durability and washfastness properties needed in textile fabric applications.